Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $174.27   13.331%   $197.5019   $197.50   $197.50   $197.50  
  Purchase #2 $166.91   9.437%   $182.6613   $182.66   $182.65   $182.70  
  Purchase #3 $40.40   7.428%   $43.4009   $43.40   $43.40   $43.40  
  Purchase #4 $72.25   6.775%   $77.1449   $77.14   $77.15   $77.10  
  Purchase #5 $183.35   11.579%   $204.5801   $204.58   $204.60   $204.60  
  Purchase #6 $78.25   12.440%   $87.9843   $87.98   $88.00   $88.00  
  Purchase #7 $52.86   6.754%   $56.4302   $56.43   $56.45   $56.40  
  7 purchase totals = $768.29       $849.7036   $849.69   $849.75   $849.70